1. Field of Invention
This invention relates to serine protease inhibitor Kazal (SPIK/SPINK/PSTI) and more specifically, its inhibitors and the use of inhibitors of SPIK as anti-cancer agents and anti-viral agents such as hepatitis B and C virus (HBV and HCV).
2. Description of Related Art
Serine protease inhibitor Kazal (SPIK) is a small protein derived from a gene with 240 base pairs that has been shown to broadly regulate the activity of many cellular proteases, such as the trypsin like proteases and chymotrypsin like proteases (1). SPIK was first discovered in the pancreas behaving as an inhibitor to prevent autoactivation of trypsinogen (2). The expression of SPIK in human liver and in other organs generally is very low. It suggests that the SPIK gene is usually inactivated in these cells. However, the expression of SPIK has been shown to increase under conditions of inflammation and cell carcinogenesis, for example, in hepatitis and the hepatocellular carcinoma (HCC) (3-7).
The reason for the over-expression of SPIK in inflammation and cancer cells is unclear. SPIK is related to cell innate defense response to virus infection. During infection such as HBV and HCV, the viral proteins induce the cell immune-response resulting in release of cytokines such as interleukin 6 (IL6), TNF-α and interferon to trigger inflammation and cell apoptotic death. Because there is an IL6 responsive element existing in the SPIK gene regulation region, the over-expression of SPIK is triggered by cytokines released during the immune response or inflammation (8, 9). SPIK is a secreted protein, which implies that at least part of the function of SPIK might be working as an anti-inflammatory protein. The anti-inflammatory nature of SPIK is supported by the fact that altering the function of SPIK by mutation triggers chronic pancreatitis (10). More importantly, our studies find that the over-expression of SPIK results in resistance to apoptotic cell death. By enhancing SPIK expression, the cells infected by virus will escape the apoptotic death triggered by immune surveillance, such as CTL-induced cell apoptosis. The fact that SPIK can bind Granzyme A, a CTL cell and NK cell released serine protease, which induces serine protease dependent cell apoptosis (SPDCA), suggests this hypothesis is relevant (11-13). As a serine protease inhibitor, SPIK can only prevent serine protease dependent cell apoptosis or SPDCA, not caspase dependent cell apoptosis or CDCA (our observation). Although CDCA is important in the clearance of virus infection, however, SPDCA might play a more important role than CDCA in the clearance of chronic virus infection (14-16), this finding is particularly significant to the ineffective clearance of infected cells during chronic viral infection. Our studies show that in HBV infected cells only SPIK, not other apoptosis inhibitors such as the CDCA inhibitors survivin and XIAP, is dramatically increased.
Since escape from immune surveillance-mediated apoptosis is a condition of cancer progression, it is understandable that active expression of SPIK results in carcinogenesis, for example, in chronic HCV and HBV infection associates closely with liver cancer. The current invention recognizes that suppressing SPIK expression will induce the apoptosis of cancer cells.
Despite the foregoing developments, there is a need in the art for inhibitors of SPIK to be used as anti-cancer agents and anti-viral agents for hepatitis B and C.
All references cited herein are incorporated herein by reference in their entireties.